firth etal



March 10, 1964 D. FIRTH ETAL 3,124,003 ISWASH PLATE TYPE ROTORY MACHINES Filed July 20, 1962 2 Sheets-Sheet 1 March 10, 1964 D. FIRTH ETAL SWASH PLATE TYPE ROTORY MACHINES 2 Sheets-Sheet 2 Filed July 20, 1962 United States Patent 3,124,008 SWAH PLATE TYPE RGTARY MACHHNES Donald Firth and Roger Harvey Yorke Hancock, East Kilbride, Glasgow, Scotland, and Michael Hobson, Horsforth, near Leeds, England, assignors to Towler Brothers (Patents) Limited Filed July 20, N62, Scr. No. 214,441 Claims priority, application Great Britain July 28, 1961 8 Claims. (Cl. 746) This invention relates to swash plate type rotary machines, whether pumps or motors.

In swash plate pumps or motors as hitherto constructed, it has been customary to mount the swash plate on trunnions or equivalent journal type bearings at either end of a diameter of the operative face of the platei.e. the surface on which the slippers bear during operation of the machine.

This arrangement has two main drawbacks. First, the overall dimensions of the machine in the direction of the axis of tilt of the swash plate must always include a significant component due to the lengths of the trunnions. Secondly, it has been found that the trunnions constitute sources of vibration and noise.

The length of a trunnion is dependent on the fatigue loading due to the oscillatory forces exerted thereon during each cycle of a cylinder and piston. These forces are of considerable magnitude so that relatively large bearing surfaces are required. Hence there is a close limit on the permissible reduction in overall dimensions of the machine along the trunnion axis.

The oscillatory forces are of suflicient magnitude and frequency to set up undesirable vibration and noise in the machine casing and associated parts, which can reach such proportions as to render the machine unsuitable for use inspite of its otherwise satisfactory hydraulic performance.

The present'invention aims at overcoming the abovementioned drawbacks and at providing a more compact machine which is less prone to noisy operation than those having trunnion-mounted swash plates. Investigations into the problem of noise of operation of these machines has revealed that a trunnion-mounted swash plate contributes a significant proportion of the total noise emitted by the machine, even when stabilising or locking struts are provided to steady the swash plate in its angular attitude of adjustment.

According to the present invention, a swash plate assembly for a swash plate type rotary machine comprises a swash plate having a rear face of which at least a substantial part is of arcuate form and a bearing member having an arcuate face slidably engaged by the arcuate face of the swash plate, whereby the angle of tilt of the swash plate can be adjusted, one of said arcuate faces being at least partly constituted by part of the curved surface of each of two similar coaxial cones disposed base-to-base and the other of said arcuate faces being of generally complementary form. The working face of the swash plate is then constituted by a plane of section including, or parallel to, the common axis of the cones.

Preferably, the meeting Zone between the conical surfaces is relieved to facilitate manufacture and assembly into the machine.

In the specification and drawings of co-pending application Ser. No. 164,423, filed January 4, 1962, there is disclosed a machine in which the swash plate has the axis of tilt off-set with respect to the point of intersection of the axis of the shaft and the working surface of the swash plate in a direction, and through a distance, such that the reaction torque on the swash plate about its axis of tilt is reduced to a minimum. In the present invention,

the location of the axis of tilt can be offset as described in the said prior specification.

A practical design of swash plate machine incorporating the invention will now be described, by way of illustration only, with reference to the accompanying drawings in which:

FIGURE 1 is a rear perspective view of a swash plate;

FIGURE 2 is a front perspective view of a seating:

FlGURE 3 is an axial section through a complete machine, and

FIGURE 4 is a diagrammatic view of control mecha nism for the swash plate.

The swash plate 1 consists essentially of a block having a plane working surface 2 which constitutes a plane of section through a pair of coaxial cones 3, 4 (FIG- URE I) placed base-to-base on a common axis 5. The axis 5 represents the axis of tilt of the swash plate, and may not, therefore, be perfectly symmetrical with the main axis of the machine for the purposes set out in the said prior specification.

The meeting zone of the cone surfaces 3, 4 is relieved, as shown at 6, to present a short cylindrical surface struck about the axis 5, and this zone is pierced at 7, 8 by a pair of elongated clearance holes for the passage of swash plate adjusting rods or jacks 9, ll) (FIGURE 3) having spherical or part-spherical heads 11 which rest in complementary sockets l2 coaxial with the clearance holes 7, 8. The swash plate 1 is pierced by a central clearance aperture 13 through which the main drive shaft 14 passes to enter the adjacent bearings 15 in the machine frame, the bearing 15 also extending into the aperture 1.

The swash plate is mounted in the machine on a bearing cup 15 having an axial aperture 17 corresponding to the aperture 13 surrounding the bearing 15. The bearing cup 16 has part-conical surfaces 18, 19 which are complernentary to the swash plate surfaces 3, 4. These are separated by a recessed cylindrical relief 20 pierced by clearance holes 21, 22 which register with the holes 7, 8 in the swash plate. The mating cone surfaces 3, 13 and 4, 19 may be left dry so as to constitute a friction damper for the oscillatory forces set up in the swash plate. However, since the latter must be tilted, and the tilting forces must be kept within practical limits, the contacting surfaces may be conventionally lubricated (and viscous shear relied upon for damping) or lined with a thin film of a dry plastic lubricant such as P.T.F.E. Alternatively, they may be impregnated with a dry lubricant such as molybdenum disulphide.

Alternatively again, however, they may be provided with a series of shallow pockets each fed with lubricant from the high pressure port of the machine through a constriction near the pocket. An advantage of the latter form of lubrication is that it can be controlled according to requirements. Thus, wh n it is required to adjust the angle of the swash plate, pressure is fed to the lubricating pockets so as to tend to float the swash plate and render its displacement easier. When the adjustment has been completed, however, the pressure in the pockets can be released, and the swash plate surfaces 3, 4 then allowed to make metal-to-metal contact with the female supporting surfaces l8, 19. Thus static friction can be used to aid in stabilising the swash plate in its required position of adjustment.

By mounting the swash plate in a cup located axially behind it, the overall diameter of the machine can be materially reduced. In fact, the body or casing of the machine need have an internal diameter little more than the external diameter of the cylinder block. For this reason the swash plate angle adjusting rods or jacks 9,19 are arranged to act on the swash plate from a position behind the plate 1.

Thus, the rods 9, 19 are provided at the opposite ends to the heads 11 with part-spherical heads 23 which rest in complementary sockets 24 in pistons 25, 26 which are reciprocable in cylinders 27, 28 respectively, the cylinders being fixed to the machine casing 2?. Secured to the piston 26 by a retaining plate 3% is the head of an axial rod 31 which extends slidably through the end wall of the cylinder 28 and has pivoted thereto outside the cylinder at 32 a valve-operating link 33. The link 33 extends transversely to the main machine axis and is shielded by a cover 34 carried by the cylinder 23. Near its midpoint the link 33 is pivoted to a spool-type valve 35 reciprocable in a valve bore to control the supply of pressure fluid to the cylinders 27, 28 and thus control the angle of the swash plate. The end of the link distant from pivot point 32 is pivoted to a control rod. In the position shown in FIGURE 4, the valve 35 seals off the working spaces in the cylinders 27, 23. These Working spaces are annular spaces 27a, 28a defined in a radial direction by the curved cylinder walls and reduced diameter extensions a, 26a of the pistons, and in an axial direction by the pistons 25, 26 and fixed sleeves 27b, 28b in which said cylinder extensions 25a, 26a are slidable. Since these working spaces are full of hydraulic fiuid, the swash plate is locked in position when they are sealed off as stated. When the control rod is moved to displace the valve to the left in FIGURE 4, pressure fluid flows through a supply pipe 36, the valve bore and duct 37 to the working space of cylinder 28. Simultaneously the working space of cylinder 27 is connected with exhaust (to the interior of the machine casing) via a pipe 38, the valve bore and ducts 39 and 46. Thus, the piston 26 is caused to move to the left and piston 25 moves to the right and the swash plate is tilted. The movement of the piston 26 causes the pivot point 32 to move to the right and thus the valve 35 is restored to its original position, locking the swash plate in position. Further movement of the control rod to the left will cause further tilting of the swash plate. If the control rod is moved to displace the valve 35 to the right, pressure fluid flows through supply pipes 36, the valve bore and the pipe 33 to the working space of cylinder 27 while simultaneously the working space of cylinder 28 is connected to exhaust through the duct 37, the valve bore, a duct 41, duct 39 and duct 49. Thus the pistons move to tilt the swash plate in the opposite direction to the direction in which it is tilted when the valve is moved to the left. The movement which occurs of piston 26 to the left causes the pivot point 22 also to move to the left so as to return the valve 35 to its original position locking the swash plate in position. It will therefore be seen that the swash plate can be locked at any desired angle of tilt by moving the control rod to an appropriate position. The right-hand ends of the cylinders are permanently connected to exhaust through ducts 42 and 43 so as not to impede movement of the pistons.

FIGURE 3 also shows other parts of the swash plate machine, e.g. the cylinder block 44 which is fixed to the shaft 14 and which contains cylinders 45 for pistons 46 having slippers 47 which bear against an annular slipper plate 48 carried by the swash plate 1. A port plate 49 is disposed between the rotatable cylinder block 44 and a fixed end block 50. These parts are illustrated only to show the swash plate mounting of the present invention in its relationship to the machine as a whole.

The cone angles of the complementary surfaces 3, 18 and 4, 19 will be chosen normally as a compromise between the positiveness of location of a large cone angle and the greater bearing area and ease of tilting of a small cone angle. It is generally assumed that an angle of 45 will be an optimum for most practical purposes.

It will, of course, be understood that the double conical male and female surfaces will not necessarily appear symmetrical about a plane containing the axis of the drive shaft 14. Asymmetry of this nature will be determined by considerations of reduction of reaction torque about the axis of tilt 5 as discussed more fully in the above-mentioned specification and drawings of application Serial No. 164,423, filed January 4, 1962.

Although the bearing cup 16 has been described and illustrated as having female conical bearing surfaces 18, 19 of comparable extent to the male surfaces 3, 4 of the swash plate 1, it will be understood that selected areas or zones thereof could be used to provide the necessary support for the swash plate 1 while the remainder is relieved. Thus, for example, each surface 13, 19 could be constituted by a bearing strip following generally the line of a generatrix of the cone. Alternatively, part annular strips may extend around the internal wall of the cup 16, their bearing surfaces forming segments of the conical surfaces 13, 19.

In the machine shown in FIGURE 3, the swash plate is constituted by the element 1 shown in FIGURE 1 and the bearing for the swash plate is constituted by the element 16 shown in FIGURE 2. If desired, the function of the elements 1 and 16 may be reversed, the element 6 being utilised as a swash plate and the element 1 as a fixed bearing therefor, by exchanging their positions in the machine.

We claim:

1. A swash plate assembly for a swash plate type rotary machine, comprising a swash plate having a rear face of which at least a substantial part is of arcuate form and a bearing member having an arcuate face slidably engaged by the arcuate face of the swash plate, whereby the angle of tilt of the swash plate can be adjusted, one of said arcuate faces being at least partly constituted by part of the curved surface of each of two similar co-axial cones disposed base-to-base and the other of said arcuate faces being of generally complementary form.

2. A swash plate assembly for a swash plate rotary machine comprising a swash plate having a rear face at least largely constituted by part of the curved surface of each of two similar co-axial cones arranged base-tobase and a bearing pad having a face of generally complementary form to said rear face of the swash plate and engaged thereby, whereby the angle of tilt of the swash plate can be adjusted by sliding the rear face thereof over said face of the bearing pad.

3. A swash plate assembly for a swash plate rotary machine, comprising a swash plate bearing member having a face at least largely constituted by part of the curved surface of each of two similar co-axial cones arranged base-to-base and a swash plate having a rear face of generally complementary form to said face of the bearing member and slidably engaged thereby, whereby the swash plate can be moved relatively to the bearing member to adjust the swash plate angle of tilt.

4. A swash plate assembly for a swash plate rotary machine, comprising a swash plate having a curved rear face and a bearing member having a curved face slidably engaged by the curved face of the swash plate, one of said curved surfaces comprising two conical portions constituted by part of the curved surface of each of two similar cones disposed base-to-base, the conical portions being separated by a cylindrical relief, and the other of said faces being of generally complementary form.

5. A swash plate assembly for a swash plate type rotary machine, comprising a swash plate having a rear face of which at least a substantial part is of arcuate form and a bearing member having an arcuate face slidably engaged by the arcuate face of the swash plate, whereby the angle of tilt of the swash plate can be adjusted, one of said arcuate faces being at least partly constituted by part of the curved surface of each of two similar co-axial cones disposed base-to-base and the other of said arcuate faces being of generally complementary form, the bearing member being provided with clearance holes and, swash plate control means being provided comprising control rods anchored at one end to the swash plate and passing through said clearance holes in the bearing member to the rear thereof and adjustable anchorages for the control rods at the rear of the bearing member.

6. A swash plate assembly according to claim 5 wherein the adjustable anchorages comprise hydraulic rams, valve means being provided controlling said rams.

7. A swash plate assembly according to claim 6 wherein the valve means is disposed side-by-side with said rams and a link extends transversely behind said bearing member coupling the valve means with one of said rams, whereby movement of the ram caused by displacement of the valve means acts to return the valve means to its original position.

8. A swash plate assembly according to claim 5 wherein the swash plate is provided with clearance holes through which said control rods pass, the rods having spherical heads at each end resting in complementary sockets in the swash plate at the end of the clearance holes therein and in complementary sockets in said adjustable anchorages.

Martin June 13, 1922 Thoma Feb. 3, 1959 

1. A SWASH PLATE ASSEMBLY FOR A SWASH PLATE TYPE ROTARY MACHINE, COMPRISING A SWASH PLATE HAVING A REAR FACE OF WHICH AT LEAST A SUBSTANTIAL PART IS OF ARCUATE FORM AND A BEARING MEMBER HAVING AN ARCUATE FACE SLIDABLY ENGAGED BY THE ARCUATE FACE OF THE SWASH PLATE, WHEREBY THE ANGLE OF TILT OF THE SWASH PLATE CAN BE ADJUSTED, ONE OF SAID ARCUATE FACES BEING AT LEAST PARTLY CONSTITUTED BY PART OF THE CURVED SURFACE OF EACH OF TWO SIMILAR CO-AXIAL CONES DISPOSED BASE-TO-BASE AND THE OTHER OF SAID ARCUATE FACES BEING OF GENERALLY COMPLEMENTARY FORM. 